4dOrganic Chemistry

Alkenes — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 4 of 18 1 quiz

📚 Edexcel Linear - OL (Chemistry) Hub / Topical Revision

0%read

Lesson summary

Alkenes Edexcel O Level Linear Chemistry notes: know that alkenes contain the functional group >C=C<Alkenes are made by cracking long-chain alkanes.First three alkenesethene, propene, butene.know that alkenes contain the functional group >C=C<know the general formula for alkenese…

Alkenes Edexcel O Level Linear Chemistry: what to do next
Unsaturated
Addition reaction
Bromine water test
Hydrogenation
Give / State / Name

Part 1 of 6Key ideas

Alkenes are made by cracking long-chain alkanes.

2First three alkenes

First three alkenes ethene, propene, butene.

Part 2 of 6Syllabus points

know that alkenes contain the functional group >C=C<

know the general formula for alkenes

explain why alkenes are classified as unsaturated hydrocarbons

understand how to draw the structural and displayed formulae for alkenes with up to four carbon atoms in the molecule, and name the unbranched-chain isomers knowledge of cis/trans or E/Z notation is not required

describe the reactions of alkenes with bromine to produce dibromoalkanes

describe how bromine water can be used to distinguish between an alkane and an alkene

Part 3 of 6Process & sequence

Alkane (long chain)
Cracking
Shorter alkane + alkene
Addition reactions

Alkanes vs alkenes

Alkanessaturated, bromine stays orange

Alkenesunsaturated, decolourise bromine water

Alkenes more reactive

Part 4 of 6Summary

Summary

Alkenes decolourise bromine water.

The general formula of alkenes is CnH2n.

Part 5 of 6Keep going

Alkenes Edexcel O Level Linear Chemistry: what to do next

These Alkenes Edexcel O Level Linear Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Alkenes Edexcel O Level Linear Chemistry understanding with the practice questions below, then reread any Alkenes Edexcel O Level Linear Chemistry point you were unsure about before moving on.

Practice: Alkenes Edexcel O Level Linear Chemistry practice questions

Previous lesson: 4c Alkanes — Notes

Next lesson: 4h Synthetic polymers — Notes

Course: Edexcel Linear – OL (chemistry) — all units

Official syllabus: Pearson Edexcel International GCSEs

Part 6 of 6Compare: Compare

Addition reactions of ethene
Reagent	Conditions	Product	Type	Use	Equation
Bromine	Room temperature	1,2-dibromoethane	Addition	Test for C=C	C₂H₄ + Br₂ → C₂H₄Br₂
Hydrogen	Ni catalyst, 150 °C	Ethane	Hydrogenation	Margarine	C₂H₄ + H₂ → C₂H₆
Steam	H₃PO₄, 300 °C, 60 atm	Ethanol	Hydration	Industrial ethanol	C₂H₄ + H₂O → C₂H₅OH
Ethene (many)	High pressure, catalyst	Poly(ethene)	Addition polymerisation	Plastic bags	n C₂H₄ → (C₂H₄)n

Key terms

Command terms

Give / State / Name

Recall a fact; one idea per mark.

Define

Give the exact meaning using the specification keywords.

Describe

Give an account of what happens / the pattern in data, quoting values; no reasons needed.

Explain

Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.

Suggest

Use knowledge in a new context; more than one answer may be accepted.

Compare

Similarities and differences; each point must refer to both items.

Calculate

Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.

Discuss

Explore the issue from different angles and link the points.

Evaluate / Assess

Weigh strengths and weaknesses and reach a supported judgement.

Deduce

Draw a conclusion from the information given.

Justify

Support a statement/choice with evidence.

Exam technique

Keywords the mark scheme looks for in this lesson

Alkene · Unsaturated · Addition reaction · Bromine water test · Hydrogenation · Hydration

Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).

Link ideas

Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.

Use the information in the question

“discuss/evaluate” answers must use the data provided and match the number of marks.

Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.

Avoid vague words

“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.

Do not extrapolate a graph line beyond the data or to zero unless asked.

Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

Last updated: 18 October 2026